The invention relates to a welding arrangement as known, for example, from the publication "Semiconductor Databook", 1981/82, page A-18, of the INTERNATIONAL RECTIFIER company. In such a welding arrangement, and to facilitate smaller and lighter welding transformers, an alternating mains current is first rectified. Subsequently, an alternating voltage having a frequency that is higher than the mains frequency is again generated from the direct voltage by use of an inverter bridge circuit constructed with four power semiconductor devices. The alternating voltage is then fed to the primary winding of a welding transformer which reduces it to a desired welding voltage.
Known arrangements of the above type are designed to be used with a specific fixed mains voltage. As a rule, they can also be operated on mains with a voltage that is smaller than the specified fixed predetermined (designated) voltage. However, in principle, it is not readily possible to operate them on mains having voltages that are higher than the specific fixed designated operating voltage. The reason for this is, in particular, that the welding transformer, owing to its magnetic and material properties, does not allow a transfer of power higher than the maximum power that is designated for its intended use. In cases where a welding arrangement designed for a lower operating voltage is to be operated on a mains with a higher voltage, it is therefore customary to connect a pretransformer or a voltage-reducing device upstream of the mains rectifier to reduce the higher mains voltage to the lower designated mains voltage. This solution is technically easy and effective and it can be realized as a modular element. This solution, however, causes correspondingly higher costs and, most of all, increases the space requirement for the welding arrangement.
For a welding arrangement of the generic type, PCT published application No. WO 9308628 published Apr. 29, 1993, corresponding to U.S. Pat. No. 5,570,254 issued Oct. 28, 1996, discloses the monitoring of the welding transformer with respect to saturation. Thus, unusually strong current rises in the primary circuit of the transformer are intended to be detected early. It is the object of the early detection of such current rises to effectively protect the expensive power semiconductor devices, that are used for realizing the inverter bridge circuit, against destruction due to oversized currents in the primary circuit.
It is therefore the object of the present invention to provide a welding arrangement having a welding transformer that is demensioned to be as small as possible, which arrangement can be operated on mains with different higher voltages.